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Resumen:
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The evolution of single-particle states in neutron-rich nuclei provides a key information on their nuclear structure and is an important ingredient for the development of nuclear models that can be applied to predict the structure at the borderline of nuclear map. The role of neutron excitations across shell gaps and the evolution proton-neutron interaction can be studied in these exotic nuclei. In particular, magic nuclei are key players for the mapping of the single-particle degrees of freedom around closed cores. A special region of interest is found around the doubly-magic 78 28Ni50. In addition, gross properties of these nuclei play a role in the astrophysical rapid neutron capture process. Nuclei in the vicinity of 78Ni have motivated recent experimental and theoretical studies, aimed at the understanding of the nuclear structure in this region with a large neutron excess. In this thesis we investigate the nuclear structure of 81;80Ga, 81Ge and 81As, populated in the decay chain of 81Zn, which was produced at ISOLDE, CERN in the framework of a systematic fast-timing investigation of neutron-rich nuclei populated in the decay of Zn. The selectivity and efficiency of the production of Zn ion beams had been previously optimized in order to guarantee the most pure beam of 77{u100000}82Zn nuclei. The estimated yield of 81Zn was 600 ions/ C giving an average activity of particles during the experiment of about 10000 counts per second. The experimental setup included two HPGe detectors, two LaBr3(Ce) detectors and a NE111A plastic scintillator for particle detection. Coincidences with the detector were used for -ray background suppression, and - coincidences between the HPGe detectors to determine the level schemes. For half-life measurements the combination of LaBr3(Ce) scintillator crystals and Time-to- Amplitude Converters was employed. The signals from the detectors were processed by a digital data acquisition (DAQ) system composed by four Pixie-4 Digital Gamma Finder cards, specially designed for -ray spectroscopy which was used for decay level schemes and the Advanced Time Delayed (“fast-timing“) (t) method employed to measure the excited level lifetimes. From the structural point of view, the isotopes under study are relatively simple systems with a few particles and/or holes outside the doubly-magic core, and thus can be treated rather successfully within the nuclear shell model...
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